Electrostatic printing



Feb. 2, 1965 M. L. LEVENE 3,153,021

ELECTROSTATIC PRINTING Filed May 1, 1961 INVENTOR. Menu 1 [El ENE- United States Patent 3,168,021 ELECTROSTATIC PRINTING Martin L. Levene, Elkins Park, Pa., assignor to Radio Corporation of America, a corporation of Delaware Filed May 1, 1961, Ser. No. 106,950 6 Claims. (Cl. 951.7)

This invention relates generally to electrostatic printing, and more particularly to improved apparatus for developing a latent electrostatic image on an electrophotographic recording element with a liquid developer.

It has been proposed to develop a latent electrostatic image on an electrophotographic recording element by passing the recording element over the top of a 11011- zontally disposed roller that rotates in an open pan filled with a liquid developer, the lower portion of the roller being immersed in the liquid developer. Because of this arrangement, it is usually not possible to observe the actual development of the latent electrostatic image, as may be desirable to control the factors in the developing process. This is especially true when the recording element 12 is in the form of a continuous web, and the developing apparatus is part of an automatic electrostatic printing system.

Much prior art electrostatic printing apparatus is also not suitable for use in a moving vehicle, such as an airplane or an automobile, because the liquid developer tends to spill out of its open container when the speed or direction of the vehicle is changed. Since some of the components of some liquid developers may produce fumes that are flammable and/ or dangerous to health, it is desirable to reduce the evaporation of these components to a minimum. While other liquid developers may not contain harmful components, they may contain components that are volatile and relatively expensive, such as trichlorotrifiuoroethane (Freon), and reduce evaporation thereof.

Accordingly, it is an object of the present invention to provide improved apparatus for developing a latent electrostatic image in a manner whereby the process of development may be observed.

It is another object of the present invention to provide improved apparatus for developing latent electrostatic images on a web of an electrophotographic recording element by means of liquid developer in a substantially closed system suitable for use in a moving vehicle.

Still another object of the present invention is to provide improved means for developing a latent image in an electrostatic printing system wherein liquid developer may be cooled conveniently to reduce the evaporation of volatile components.

A further object of the present invention is to provide improved means for developing latent electrostatic images, said means being relatively simple in construction and operation, easy to manufacture, and highly efficient in use.

Briefly, the improved apparatus of the present inven tion comprises improved means for developing a latent electrostatic image on the surface of an electrophotographic recording element by means of a liquid developer. The improved means comprises a tubular member whose longitudinal axis is adapted to be disposed in an upright position, or at a predetermined angle to the horizontal, during normal operation. The tubular member has a wall formed with one or more openings in it so that liquid developer introduced into the interior of the tubular member emerges through these openings. Means are also provided to move the exposed electrophotographic recording element adjacent to these openings so that the liquid developer emerging from the openings develops the latent electrostatic image. The liquid developer draining from the recording element is collected by suitable means so that the developer may be used again. The liquid developer may be circulated in a substantially closed systerm that lends itself easily to refrigeration, thereby reducing the rate of evaporation of the volatile components of the developer.

The novel features of the present invention, both as to its organization and operation, as well as additional objects and advantages thereof, will be described in greater detail with reference to the accompanying drawing, the single figure of which is a perspective view of an electrostatic printing system, including the improved developing apparatus of the present invention, portions of the developing apparatus being represented schematically.

Referring, now, to the drawing, there is shown an electrostatic system 10 for developing latent electrostatic images that may be placed on an electrophotographic recording element 12. The recording element 12 may comprise a web of paper, one surface of which is coated with a layer (not shown) of photoconductive material, such as zinc oxide. The photoconductive layer on the recording element 12 is on the far side of the recording element 12, as viewed in the drawing. The recording element 12, originally wound on a roll 14, is connected to a take-up roll 16. A motor 18, connected to a shaft 29 of the take-up roll 16, is arranged to rotate the take-up roll 16 so as to unwind the recording element 12 from the roll 14 and to wind it on the take-up roll 16.

Means are provided to charge the photoconductive layer of the recording element 12 with a uniform electrostatic charge. To this end, a corona discharge device 22 is connected to a high voltage (about 6,000 volts), unidirectional power supply Zd, in a known manner, to cause a uniform negative electrostatic charge to be deposited on the recording element 12. The uniformly charged portion of the recording element 12 may now be exposed by a light image from a projector 26 to produce a latent electrostatic image, within the dashed rectangle 28, on the recording element 12. It will be understood that the recording element 12 may be advanced continuously or intermittently by the motor 18, as necessary.

To develop the latent electrostatic image, the recording element 12 is moved, by the motor 13, across the improved developing apparatus 36 of the present invention.

The developer apparatus 39 comprises a tubular member 32, such as a hollow cylinder.

The tubular member 32 is positioned so that its longitudinal axis is at a predetermined angle to the horizontal during normal operation. As shown in the drawing, the tubular member 32 axis is in a substantially vertical plane, that is, at an angle of degrees to the horizontal. It will be understood, however, that the member 32 may be disposed at an acute angle to the horizontal, if so desired. The angle which will permit liquid developer to run off the recording element 12 at a desired rate, when in contact with the tubular member 32, in a manner to be hereinafter explained, is one of the factors determining the size of the angle.

The [tubular member 32. has a cylindrical wall 34 formed with a plurality of linearly aligned, small openings 36 therein. Each of the openings 36 communicates with the interior of the hollow tubular member 32. The locus of the aligned holes 3:; defines a straight line substantially parallel to the axis of the tubular member 32.

Means are provided to direct a liquid developer into the interior of the tubular member 32. To this end, a tank 38 of liquid developer is cormected to the interior of the tubular member 32 by means of a pipe 40, represented schematically in part, and a pump 42. The pipe 49 is connected to the interior of the tubular member 32 through an upper end wall 44 of the tubular member. it will now be understood that at least some of the liquid developer introduced into the interior of the tubular member 32 will escape through the openings 36 in the cylindrical wall 34.

The liquid developer emerging through the openings 36 contacts the exposed photoconductive layer of the recording element 12 and develops the latent electrostatic image thereon. Since the recording element 12 is disposed in a substantially vertical plane, the liquid developer 46 drains off the recording element 12 into a sump 48. The sump 48 should be only as large "as necessary to collect the liquid developer that drains from the recording element 12, in order to prevent excessive evaporation of the liquid developer. To this end, portions of the sump 43 should be covered by any suitable cover means (not shown). A pipe 5% connects the bottom of the sump 43 with the tank 38 so that the used liquid developer may be recirculated through the tubular member 32.

The recording element 12 is spaced from the wall 34 of the tubular member, adjacent to the openings 36, by upper and lower shims 52 and 54, respectively. The shims 42 and 54 are fixed to the tubular member 32 by any suitable means and are spaced so as to contact the upper and lower edges of the recording member 12. It will now be understood that as the recording element 12 moves past the openings 36 in the cylindrical wall 34, liquid developer 46 emerging from the openings 36 forms a thin film between the Wall 34 and the recording element 12, whereby to develop the latent electrostatic image thereon. The speed of the motor 18 is adjusted by any suitable means (not shown) so as to control the developing time of the recording element 12. Since the recording element 12 is developed in a substantially vertical plane, the development process may be observed easily, and the time of development, for example, may be controlled in accordance with observed results. Also, the design of the developing equipment is more flexible if it is not restricted to development of a horizontally disposed Web.

After development, the developed image on the recording element 12 is moved pasta heater 56 to fuse the developer pigments of the developer 46, whereby to provide a fixed image on the recording element 12, if necessary. The heater 56 may also function to dry the recording element 12 by evaporating the volatile components of the developer 46. Thus, there has been provided, in an electrostatic printing system, improved developing. apparatus which enables one to observe the actual development of an electrostatic image during the process of its development. The improved developing apparatus is substantially a closed system wherein excessive evaporation of the liquid developer can be prevented. Because the liquid developer is circulated through the developer apparatus over and over again, it is economical and convenient to refrigerate the liquid developer, as by a refrigerator 53 including cooling coils associated with the tank 38 and the sump 48, to reduce further losses by evaporation. Since portions of the improved apparatus of the present invention have been shown in diagrammatic form, variations in the apparatus coming within the spirit of the invention will readily suggest themselves to those skilled in the art. Hence, it is desired that the foregoing shall be considered merely illustrative and not in a limiting sense.

What is claimed is:

1. Means for developing an electrostatic image on an electrophotographic recording element with a liquid developer, said means comprising a tubular member whose longitudinal axis is disposed at an angle other than zero with respect to the horizontal, said tubular member having a Wall formed with a plurality of substantially linearly aligned openings communicating with the interior of said member, means connected to one end of said tubular member to direct said liquid developer into said tubular member so that said developer may flow through said openings, means to move said element adjacent to said openings in said wall with said electrostatic image facing said openings whereby said developer may contact and develop said image, means to collect an excess port-ion of said developer after said developer has contacted said image, and means connecting said last-mentioned means to said developer directing means so that said last-mentioned means to said developer directing means so that said developer may be re-used.

2. Means for developing an electrostatic image on an electrophotographic recording element with a liquid developer, said means comprising a tubular member whose longitudinal axis is disposed at an angle other than zero With respect to the horizontal, said member having a wall formed with a plurality of linearly aligned openings substantially parallel to said axis and communicating with the interior of said member, means connected adjacent one end of said member to direct said liquid developer. into said interior of said tubular member so that at least some of said developer may flow from said interior through said opening, means to move said element past said openings in said wall with said electrostatic image facing said openings at a predetermined distance therefrom so that said developer may contact and develop said image, means to collect excess of said developer adjacent the other end of said member after said developer has contacted said image, and means connected to said last-mentioned means to transfer said developer to said one end of said member for re-use.

3. In an electrostatic printing system wherein an electrophotographic recording element in the form of a sheet is electrostatically charged and exposed to produce an electrostatic image thereon, means to develop said image with a liquid developer comprising a tank for said developer, a tubular member having an axis disposed at a predetermined angle to the horizontal, means to circulate said developer from said tank, through said tubular member and back to said tank, said tubular member having a wall formed with a plurality of openings therein communicating with the interior of said member so that said developer may pass through said openings, means to move said sheet adjacent to said openings and at a predetermined distance therefrom with said image adjacent to said openings to develop said image, means to collect excess developer draining from said sheet, and means to refrigerate said excess developer and developer in said tank.

4. Electrophotographic apparatus comprising: means for transporting an elecrophotographic recording element along a predetermined path with a recording surface thereof substantially vertically disposed; an elongated electrostatic charging unit substantially vertically disposed adjacent said path for charging said recording surface; exposure means for projecting a light image onto said recording element in said path to produce on said recording surface an electrostatic latent image; and developer means comprising a hollow member having a wall formed with at least one opening communicating with the interior thereof, means connected to said member to direct liquid developer composition into said interior of said member so that developer composition may be discharged from said interior through said opening, means positioning said hollow member With said wall substantially vertically disposed adjacent said path so that developer composition discharged through said opening may develop said latent image.

5. Electrophotographic apparatus comprising: means for transporting electrophotographic sheet material along a predetermined path with a recording surface thereof substantial-1y vertically disposed; at least one corona generating wire substantially vertically disposed adjacent said path for electrostatically charging said recording surface;

168115 for projecting a light image onto said sheet material in said path to produce an electrostatic latent image on said recording surface; developer means for developing said electrostatic latent image with a liquid developer composition, said developer means including an elongated surface substantially vertically disposed adjacent said 9 path, means spacing said recording surface a predetermined distance from said elongated surface and means for injecting liquid developer composition into the space between and in contact with both said recording surface and said elongated surface; and means adjacent said path for drying said recording surface.

6. Eleotrophotographic apparatus comprising means for transporting electrophotographic sheet material along a predetermined path with a recording surface thereof substantially vertically disposed, a charging device including at least one corona generating Wire substantially vertically disposed adjacent said path for charging said recording surface, exposure means for projecting a light image onto said path to produce an electrostatic latent image on said recording surface, a tubular member having a Wall formed with a plurality of openings communicating With the interior thereof, said openings being substantially vertically aligned adjacent said path, means connected to said tubular member to direct liquid developer composition into said interior to discharge through said openings, means to space said sheet material a predetermined distance from said Wall and said openings to cause said discharged developer composition to flow across said recording surface and develop said latent image thereon, means positioned below said tubular member for collecting excess developer composition draining from said 6 recording surface, and means for recirculating collected eveloper composition through said tubular member.

References Cited by the Examiner UNITED STATES PATENTS 2,221,776 1 1/ Carlson. 2,685,536 8/54 Starkey et a1. 117-93.4 2,691,260 10/54 Schlemmer. 2,723,923 11/55 Munters 118602 2,774,679 12/ 5 6 Remer 1'17102 2,796,847 6/57 Guggenheim 118-411 2,942,787 6/60 Bok et al 239138 X 2,960,064 11/60 Norton 1183 25 X 2,991,754 7/61 Johnson 118637 X 3,005,726 10/61 Olson 11737 3,038,073 6/62 Johnson. 3,051,044 8/62 McNane 95-1 .7 X 3,073,721 1/63 Pokorny 117119.2 X 3,096,198 7/63 Schaffert 118637 X FOREIGN PATENTS 447,219 5 /3 6 Great Britain.

728,745 4/55 Great Britain.

834,25 5 3 Great Bnitain.

WILLIAM D. MARTIN, Primary Examiner.

Patent No 3,168 ,021 February 2 1965 Martin L. Levene It is hereby certified that err en't requiring correction and that th corrected below or appears in the above numbered pate said Letters Patent should read as Column 4, lines 5 and 6, strike out "said last-mentioned means to said developer directing means so that".

Signed and sealed this 29th day of June 1965.

(SEAL) Atlest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,168,021 February 2, 1965 Martin L, Levene It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, lines 5 and 6, strike out "said last-mentioned means to said developer directing means so that".

Signed and sealed this 29th day of June 1965.

(SEAL) Atlest:

ERNEST W. SWIDER' EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

5. ELECTROPHOTOGRAPHIC APPARATUS COMPRISING: MEANS FOR TRANSPORTING ELECTROPHOTOGRAPHIC SHEET MATERIAL ALONG A PREDETERMINED PATH WITH A RECORDING SURFACE THEREOF SUBSTANTIALLY VERTICALLY DISPOSED; AT LEAST ONE CORONA GENERATING WIRE SUBSTANTIALLY VERTICALLY DISPOSED ADJACENT SAID PATH FOR ELECTROSTATICALLY CHARGING SAID RECORDING SURFACE; MEANS FOR PROJECTING A LIGHT IMAGE ONTO SAID SHEET MATERIAL INSAID PATH TO PRODUCE AN ELECTORSTATIC LATENT IMAGE ON SAID RECORDING SURFACE; DEVELOPER MEANS FOR DEVELOPING SAID ELECTROSTATIC LATENT IMAGE WITH A LIQUID DEVELOPER COMPOSITION, SAID DEVELOPER MEANS INCLUDING AN ELONGATED SURFACE SUBSTANTIALLY VERTICALLY DISPOSED ADJACENT SAID PATH, MEANS SPACING SAID RECORDING SURFACE A PREDETERMINED DISTANCE FROM SAID ELONGATED SURFACE AND MEANS FOR INJECTING LIQUID DEVELOPER COMPOSITION INTO THE SPACE BETWEEN AND IN CONTACT WITH BOTH SAID RECORDING SURFACE AND SAID ELONGATED SURFACE; AND MEANS ADJACENT SAID PATH FOR DRYING SAID RECORDING SURFACE. 